Browsing by Author "Aydin, Harun"

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Comprehensive Natural Radioactivity and Pollution Risk Assessments of Aquatic Media and Sediment in Lake Van (T?rkiye)
(Pergamon-elsevier Science Ltd, 2023) Zorer, Ozlem Selcuk; Yorgun, Nergiz Yildiz; Ozdemir, Omer Faruk; Ogun, Erdal; Aydin, Harun; Atici, Ataman Altug; Elp, Mahmut
This paper studies the radionuclide (137Cs, 226Ra, 232Th, 40K) activity concentrations and gross radioactivities in waters and sediments of Lake Van, which is the third largest closed lake (with no natural or artificial outlet) within the Earth. The physico-chemical parameters were measured and evaluated in the lake waters. The mean gross alpha activities in surface, middle and bottom waters are 0.04, 0.03 and 0.03 Bq/L, respectively, and in the same order, the mean gross beta activities are 0.30, 0.23 and 0.33 Bq/L, respectively. In sediment samples, the mean activity concentrations were measured as 1.98 Bq/g for gross-alpha, 3.46 Bq/g for gross-beta, 48.3 Bq/kg for 226Ra, 32.0 Bq/kg for 232Th, 540.1 Bq/kg for 40K and 25.9 Bq/kg for 137Cs. The radiation hazard parameters values based on the measured activities were calculated and Raeq values are lower than the world average value in all samples, while Dout and AED values are relatively high in some sediment samples.
Effects of Sinuosity Factor on Hydrodynamic Parameters Estimation in Karst Systems: a Dye Tracer Experiment From the Beyyayla Sinkhole (Eskisehir, Turkey)
(Springer, 2014) Aydin, Harun; Ekmekci, Mehmet; Soylu, Mehmet Evren
The sinuosity factor (SF) is a critical value in karst systems in terms of estimating their hydrodynamic parameters including groundwater velocity, coefficient of dispersion, etc., through dye tracer experiments. SF has been used in a number of different dye tracer experiments in karstic systems to estimate a representative flow path. While knowing SF is crucially important in the estimation of hydrodynamic parameters, its calculation is associated with significant uncertainty due to the complexity of subsurface karstic features. And yet, only a few studies have discussed its uncertainties, which might lead some errors in estimation of hydrodynamic parameters from dye tracer experiment. In this study, dye tracer experiments were conducted in two consecutive years (2003 and 2004) representing low and high flow conditions in the Beyyayla sinkhole (Eskisehir, Turkey) where the flow path is well known. Uranine was used in experiments as a tracer and QTRACER computer program was used to determine the hydrodynamic properties of the Beyyayla karst system as well as to gain insights into the effects of SF from dye tracer experiments on estimated parameters. The results showed that the breakthrough curve follows a unimodal and a bimodal distribution in low and high flow conditions, respectively. These different distributions stem from the water transport mechanisms, where velocities were calculated as 58.2 and 93.6 m h(-1) during low and high flow conditions observed in a spring emerging from the south side of the studied system. The results also show that the coefficient of dispersion, Reynolds number, and Peclet number increased and longitudinal dispersivity decreased with the higher flow rate. Furthermore, the estimated parameters did not vary with either the flow conditions or the tracer transit time, but they have shown some variations with SF. When SF was increased by 50 %, a change in these parameters was obtained in the range of 50-125 %.
Estimation of Evaporation for Lake Van
(Springer, 2016) Aydin, Harun; Karakus, Huseyin
An evaporation study was conducted at Van Lake, one of the largest soda lakes on Earth, which is located on a high plateau in the Eastern Anatolia region of Turkey. Evaporation on a daily basis for the Gevas, station located at the southeastern shore of the lake was calculated using the Bowen ratio energy budget (BREB), Priestley-Taylor, deBruin-Keijman, Penman, and deBruin methods. The calculated evaporation values were then compared and tested with previously calculated and measured evaporation rates. Compared with available measured evaporation data, the best evaporation estimations (within +/- 0.5 mm/day) were made by the BREB method. The BREB calculations made in this study were statistically significant at the confidence level of 99.9 % for estimation of evaporation at the Gevas, station. Relationships between the calculated BREB evaporations and historical climatic records were also examined to propose a new empirical equation for evaporation estimation for the case of Lake Van. The best regression equation with a coefficient of determination (R-2) of 0.9399 was found between BREB evaporation values and incoming solar radiation (Qs) values. A power regression model proposed to estimate daily evaporation rates from Qs values was statistically significant at the confidence level of 99.9 %. Additionally, a few regression models were also examined to predict the surface water temperature of Lake Van from recorded air temperature. The highest coefficient of determination (0.974) and moderate standard error (3.12 degrees C) values were obtained from a polynomial air-water temperature model. Estimated lake water temperatures using the polynomial model were within +/- 10 % of observed lake water temperatures.
Hnc-Plot: an Excel Vba for Visualization of Helium, Nitrogen and Co2 Isotope Data of Crustal and Mantle Gases
(Springer Heidelberg, 2017) Karakus, Huseyin; Aydin, Harun
We present HNC-Plot, an Excel Visual Basic Application (Excel VBA) that can easily be used to create graphical plots of fluids associated with volcanic gases or geothermal manifestations, based on their helium, nitrogen and CO2 isotope data. HNC-Plot has been designed in a simple way; all the user has to do is to input data in an Excel spreadsheet. The spreadsheet also contains buttons which have links to Excel VBA codes that generate plots. Once, the respective button is clicked, and all required variables are defined, Excel VBA generates a plot with labels and axes. Based upon the user preferences, additional tasks such as construction of mixing lines between mantle and crustal gases or calculation of end-member proportions can also be performed. We sincerely believe geoscientists can quickly and easily create these plots, free of charge, with this application. This study also presents previously published data from related literature to show the foundations of the application and to present sample plots created with it.
A Hydrologic Restoration Attempt of the Dried Akgol Wetland (Central Anatolia, Turkey)
(Springer, 2017) Karakus, Huseyin; Aydin, Harun; Erdem, Osman
The Akgol Wetland has been subject to extensive drainage processes by anthropogenic factors that have almost caused the wetland to disappear since the 1970s. In this contribution, as a one of the pioneering work on wetland restoration in Turkey, we present hydrological studies aiming to restore the natural function of the Akgol wetland and post-restoration observations. Considering the water budget of the wetland, three scenarios focusing on restoring the wetland hydrology were developed. The open water surface area and volumetric water storage relations for each scenario were simulated using GIS-based tools. The most appropriate scenario for restoration of the Akgol Wetland was chosen by taking the original state of the wetland prior to drainage as the primary criterion. As the first stage, functioning of the central channel draining the wetland was ceased by refilling it. Following this, an artificial bank was constructed at the narrowest part of the wetland, which resulted in an open water surface that cover all current and former ponds. The wetland has start to hold surface runoff and groundwater inflows since September 2011. Since rewetting, the Akgol Wetland is regaining its ecosystem functions and the increase in avian population indicate the proposed restoration effort was successful.
Mineralogical and Chemical Characterization of Acidic Pumices Outcrop North of Lake Van
(Iop Publishing Ltd, 2016) Yucel, Aysegul; Efe, Tugba; Onal, Mehmet; Depci, Tolga; Aydin, Harun
In the present study, mineralogical, physical and chemical characteristics of the pumice located in North of Lake Van locations were investigated to find an applicability of them for cement and textile industry. Characterization studies of the pumice samples were carried out by thin section, SEM, XRF, XRD and FTIR analysis. In addition, the bulk density, Hard Grove Index (HGI), pozzolanic activity and reactive silica of the pumice samples were determined. The overall results showed that the pumice samples, which might be an eruption product of Mount Suphan, had an amorphous structure and rhyolite composition in high calcalkaline series. The chemical compositions and physical properties indicated that the pumice samples could be used in cement and textile industry.
Post-Earthquake Anomalies in He-Co2 Isotope and Relative Abundance Systematics of Thermal Waters: the Case of the 2011 Van Earthquake, Eastern Anatolia, Turkey
(Elsevier, 2015) Aydin, Harun; Hilton, David R.; Gulec, Nilgun; Mutlu, Halim
We report the helium and carbon isotope (He-3/He-4, delta C-13) and relative abundance (CO2/He-3) characteristics of hydrothermal gases from eastern Anatolia sampled similar to 1 month after the October 23, 2011 Van earthquake (Mw: 7.2, focal depth: 19 km). Seven sites were sampled which comprise three localities along the Caldiran Fault Zone, at a distance of 58-66 km to the epicenter (Group I), two localities north of the Caldiran Fault, about 90-113 km from the epicenter (Group II), and two localities in the vicinity of the historically-active Nemrut Caldera at a distance of 110-126 km from the epicenter (Group III). All sites were previously sampled for their He-CO2 systematics in 2009 (Mutlu et al., 2012) facilitating direct comparison with the post-earthquake dataset. The post-earthquake values cover a wide range of He-3/He-4, delta C-13 and CO2/He-3 ratios, from 0.84 to 6.37 RA (where RA = air He-3/He-4), -5.30 to + 0.49% (vs. VPDB), and 4.9 x 10(10) to 6.85 x 10(13), respectively. Group I samples show a consistent post-earthquake increase in He-3/He-4 whereas both Group II localities decreased in He-3/He-4. No change was recorded for the two Group III localities. He isotope variations are consistentwith simple changes in the proportions of mantle and crustal volatiles, with all Group I sites showing an increase in the mantle He contribution. We hypothesize that the enhanced mantle He signal is derived from asthenospheric melts intruded into the crust, with seismic perturbations responsible for bubble formation and growth leading to overpressure and gas loss. The strike-slip Caldiran Fault Zone provides the permeable pathway for the liberated volatiles to reach hydrothermal systems at shallow levels of the crust and the surface. Release of crustal He dominates the He mass balance of Group II samples as locations are further from the earthquake epicenter. Group III samples are even further away from the earthquake and show no perturbations in He isotopes. Whereas binary mixing dominates the He isotope systematics, CO2 shows additional effects involving the hydrothermal system. Consequently, changes in the balance between mantle and crustal CO2 are masked and more difficult to discern. The results emphasize the sensitivity of He isotopes to seismic perturbations in the crust and illustrate how location of sampling sites - on permeable segments of faults - and distance from seismic events influence resulting changes involving gas chemistry. (C) 2015 Elsevier B.V. All rights reserved.
The Salinity Problem at Yelkoma Lagoon (yumurtalik-Adana) and Its Restoration by Mixing With Freshwater From Ceyhan River
(Parlar Scientific Publications (p S P), 2015) Aydin, Harun; Karakus, Huseyin; Erdem, Osman
The Yelkoma Lagoon located at Ceyhan River Delta has been significantly deteriorated due to dam construction activities that cause lower freshwater inputs. Compared to the Mediterranean (similar to 40 ppt), high salinity of the Yelkoma Lagoon (up to 116.0 ppt), has adversely affected the ecological life in the lagoon as evidenced by the number of fish deaths. In addition to less freshwater input, high evaporation rates and structure of the inlet channel between the lagoon and the Mediterranean are determined as major causes of high salinities. In this study, we applied End-Member Mixing Analysis to calculate the monthly amount of freshwater that should be contributed from the Ceyhan River to the Yelkoma Lagoon to decrease salinity and ensure sustainability of ecological life and fisheries. As a first stage of the study, a conceptual hydrological model of the Yelkoma Lagoon has been developed based on water volume and its salinity. A bathymetric map of the lagoon was produced allowing measurement of the area and volume of each sector in the lagoon. Monthly salinities were obtained from field surveys for all components of mixing equations. The optimum salinity of the lagoon water has been foreseen to be between the salinity of the Ceyhan River and the Mediterranean. Based on the conceptual model and using a mass balance equation, contributions of saline and freshwater end-members were calculated. As a result of mixing calculations, monthly required flow-rates of freshwater from the Ceyhan River to the Yellcoma Lagoon were determined to be in the range of 0.199 m(3)/s to 3.698 m(3)/s. The calculated freshwater has been given to the lagoon since March 2009, and positive developments have been observed in terms of ecological life.
Spatial Variations in Gas and Stable Isotope Compositions of Thermal Fluids Around Lake Van: Implications for Crust-Mantle Dynamics in Eastern Turkey
(Elsevier, 2012) Mutlu, Halim; Gulec, Nilgun; Hilton, David R.; Aydin, Harun; Halldorsson, Saemundur A.
We investigate the helium (He-3/He-4) and carbon (delta C-13) isotope compositions and relative abundance ratios (CO2/He-3) of gas samples together with the stable isotope compositions of dissolved carbon and sulfur and the oxygen and hydrogen isotopic compositions of the associated water phase from a number of geothermal fields located around Lake Van in eastern Anatolia, Turkey. The mantle-derived helium component, which is likely transferred to the crust beneath eastern Turkey by recent magmatism, is found to constitute up to 96% (e.g. Nemrut Caldera) of the total He content in fluids. As regards the spatial distribution of He, samples collected from areas of Pliocene-Quaternary volcanics are characterized by a wide and generally higher range of R/R-A ratios (0.93 to 7.76 R-A) compared to those of non-volcanic regions ((1.85 to 1.0 R-A). CO2/He-3 ratios vary over a wide range (2.4 x 10(5)-3.8 x 10(13)) but are mostly higher than that of the nominal upper mantle (similar to 2 x 10(9)). Oxygen-hydrogen isotope values of the waters are conformable with the Global Meteoric Water Line and indicate a local meteoric origin. Sulfate in waters is most probably derived from dissolution of marine carbonates and terrestrial evaporite units. Temperatures calculated by SO4-H2O isotope geothermometry lie between 40 and 199 degrees C, and are in poor agreement with reservoir temperatures estimated from silica geothermometers. Discordant temperatures may be due to either the relatively slow rate of isotopic equilibrium between water and sulfate or mixing of geothermal water with sulfate-bearing shallow waters which may modify the delta O-18 value. The delta C-13 (CO2) values of gas samples are consistently lower than those of their water counterparts, consistent with loss of CO2 from waters by degassing. Mixing between mantle and various crustal C-sources appears to be the main control on the C-isotope composition. The principal origin of CO2 in all samples is crustal lithologies, mainly limestone (similar to 85 to 98% of the total carbon inventory): thus, the crustal carbon flux is at least 10 times that from the mantle. There is a broad correlation between high He-3/He-4 values and thinner crust in the western part of the Lake Van region, where several historically-active volcanoes are located. This observation indicates that localized volcanic and magmatic activity exerts the primary control on the balance between mantle and crustally-derived volatiles in the region. (C) 2012 Elsevier B.V. All rights reserved.
Sunshine-Based Estimation of Global Solar Radiation on Horizontal Surface at Lake Van Region (Turkey)
(Pergamon-elsevier Science Ltd, 2012) Duzen, Hacer; Aydin, Harun
In this study several sunshine-based regression models have been evaluated to estimate monthly average daily global solar radiation on horizontal surface of Lake Van region in the Eastern Anatolia region in Turkey by using data obtained from seven different meteorological stations. These models are derived from Angstrom-Prescott linear regression model and its derivatives such as quadratic, cubic, logarithmic and exponential. The performance of this regression models were evaluated by comparing the calculated clearness index and the measured clearness index. Several statistical tests were used to control the validation and goodness of the regression models in terms of the coefficient of determination, mean percent error, mean absolute percent error, mean biased error, mean absolute biased error, root mean square error and t-statistic. The results of all the regression models are within acceptable limits according to the statistical tests. However, the best performances are obtained by cubic regression model for Bitlis, Gevas, Hakkari, Mus stations and by quadratic regression model for Malazgirt, Tatvan and Van stations to predict global solar radiation. The spatial distributions of the monthly average daily global solar radiation around the lake Van region were obtained with interpolation of calculated solar radiation data that acquired from best fit models of the stations. The annual average solar energy potential for Lake Van region is obtained between 750 kWh/m(2) and 2485 kWh/m(2) with annual average of 1610 kWh/m(2) (C) 2012 Elsevier Ltd. All rights reserved.